Light modulation device

ABSTRACT

A light modulation device is disclosed herein. In some embodiments, a light modulation device includes a first polymer film substrate, a second polymer film substrate, an active liquid crystal layer disposed between the first and second polymer film substrates, wherein the active liquid crystal layer is capable of switching between a vertical orientation state and a twisting orientation state upon application of a voltage, each of the first and second polymer film substrates has an in-plane retardation of 4,000 nm or more for light having a wavelength of 550 nm, a ratio of an elongation (E1) in a first direction to an elongation (E2) in a second direction perpendicular to the first direction of 3 or more, and wherein an angle formed by the first directions of the first and second polymer film substrates is in a range of 0 degrees to 10 degrees.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a national phase entry under 35 U.S.C. § 371of International Application No. PCT/KR2018/005020, filed on Apr. 30,2018, which claims priority from Korean Patent Application No.10-2017-0054964 filed on Apr. 28, 2017, Korean Patent Application No.10-2018-0003783, Korean Patent Application No. 10-2018-0003784, KoreanPatent Application No. 10-2018-0003785, Korean Patent Application No.10-2018-0003786, Korean Patent Application No. 10-2018-0003787, KoreanPatent Application No. 10-2018-0003788, Korean Patent Application No.10-2018-0003789, filed on Jan. 11, 2018, and Korean Patent ApplicationNo. 10-2018-0004305 filed on Jan. 12, 2018, the disclosures which areincorporated by reference herein.

TECHNICAL FIELD

This application relates to a light modulation device.

BACKGROUND ART

A light modulation device, in which a light modulation layer including aliquid crystal compound or the like is positioned between two substratesfacing each other, has been used for various applications.

For example, in Patent Document 1 (EP Patent Application Publication No.0022311) a variable transmittance device using a so-called GH cell(guest host cell), in which a mixture of a liquid crystal host materialand a dichroic dye guest is applied, as a light modulation layer hasbeen known.

In such a device, a glass substrate having excellent optical isotropyand good dimensional stability has mainly been used as the substrate.

There is an attempt to apply a polymer film substrate instead of a glasssubstrate as a substrate of the light modulation device, while theapplication of the light modulation device is extended to eyewear or asmart window such as a sunroof without being limited to the displaydevice and the shape of the device is not limited to a plane, butvarious designs such as a folding form are applied thereto, with showingthe necessity of a so-called flexible device or the like.

In the case of applying the polymer film substrate, it is known that itis advantageous to apply a film substrate which is as opticallyisotropic as possible and has a small difference in physical propertiesin so-called MD (machine direction) and TD (transverse direction)directions in order to secure characteristics similar to those of aglass substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an exemplary light modulation device ofthe present application.

FIG. 2 illustratively shows eyewear.

FIGS. 3 and 4 show durability evaluation results for Examples andComparative Examples.

DISCLOSURE Technical Problem

The present application relates to a light modulation device. It is anobject of the present application to provide a light modulation devicewhich is excellent in both mechanical properties and optical propertiesby applying an optically and mechanically anisotropic polymer film as asubstrate.

Technical Solution

In this specification, the term such as vertical, horizontal, orthogonalor parallel among terms defining an angle means substantially vertical,horizontal, orthogonal or parallel in the range without impairingintended effects, and the range of vertical, horizontal, orthogonal orparallel includes an error such as a production error or a deviation(variation). For example, each case of the foregoing may include anerror within about ±15 degrees, an error within about ±10 degrees or anerror within about ±5 degrees.

Among physical properties mentioned herein, when the measuredtemperature affects relevant physical properties, the physicalproperties are physical properties measured at room temperature, unlessotherwise specified.

In this specification, the term room temperature is a temperature in astate without particularly warming or cooling, which may mean onetemperature in a range of about 10° C. to 30° C., for example, atemperature of about 15° C. or higher, 18° C. or higher, 20° C. orhigher, or about 23° C. or higher, and about 27° C. or lower. Unlessotherwise specified, the unit of the temperature mentioned herein is °C.

The phase difference and the refractive index mentioned herein mean arefractive index for light having a wavelength of about 550 nm, unlessotherwise specified.

Unless otherwise specified, the angle formed by any two directions,which is mentioned herein, may be an acute angle of acute angles toobtuse angles formed by the two directions, or may be a small angle fromangles measured in clockwise and counterclockwise directions. Thus,unless otherwise specified, the angles mentioned herein are positive.However, in order to display the measurement direction between theangles measured in the clockwise direction or the counterclockwisedirection if necessary, any one of the angle measured in the clockwisedirection and the angle measured in the counterclockwise direction maybe represented as a positive number, and the other angle may berepresented as a negative number.

The liquid crystal compound included in the active liquid crystal layeror the light modulation layer herein may also be referred to as liquidcrystal molecules, a liquid crystal host (when included with thedichroic dye guest), or simply liquid crystals.

The present application relates to a light modulation device. The termlight modulation device may mean a device capable of switching betweenat least two or more different light states. Here, the different lightstates may mean states in which at least the transmittance and/or thereflectance are different.

An example of the state that the light modulation device can implementincludes a transmission mode state, a blocking mode state, a highreflection mode state and/or a low reflection mode state.

In one example, the light modulation device, at least, may be a devicecapable of switching between the transmission mode and blocking modestates, or may be a device capable of switching between the highreflection mode and low reflection mode states.

The transmittance of the light modulation device in the transmissionmode may be at least 20% or more, 25% or more, 30% or more, 35% or more,40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% ormore, 70% or more, 75% or more, or 80% or more or so. Also, thetransmittance of the light modulation device in the blocking mode may be60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% orless, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less,or 5% or less. Since the higher the transmittance in the transmissionmode state is, the more advantageous it is and the lower thetransmittance in the blocking mode state is, the more advantageous itis, the upper limit of the transmittance in the transmission mode stateand the lower limit of the transmittance in the blocking mode state arenot particularly limited, where in one example, the upper limit of thetransmittance in the transmission mode state may be about 100% and thelower limit of the transmittance in the blocking mode state may be about0%.

On the other hand, in one example, in the light modulation devicecapable of switching between the transmission mode state and theblocking mode state, the difference between the transmittance in thetransmission mode state and the transmittance in the blocking mode state(transmission mode−blocking mode) may be 15% or more, 20% or more, 25%or more, 30% or more, 35% or more, or 40% or more, or may be 90% orless, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less,60% or less, 55% or less, 50% or less, or 45% or less.

The above-mentioned transmittance may be, for example, linear lighttransmittance. The linear light transmittance is a percentage of theratio of the light transmitted in the same direction as the incidentdirection to the light incident on the device. For example, if thedevice is in the form of a film or sheet, the percentage of the lighttransmitted through the device in the direction parallel to the normaldirection among the light incident in a direction parallel to the normaldirection of the film or sheet surface may be defined as thetransmittance.

The reflectance of the light modulation device in the high reflectionmode state may be at least 10% or more, 15% or more, 20% or more, 25% ormore, 30% or more, 35% or more, or 40% or more. Also, the reflectance ofthe light modulation device in the low reflection mode state may be 20%or less, 15% or less, 10% or less, or 5% or less. Since the higher thereflectance in the high reflectance mode is, the more advantageous it isand the lower the reflectance in the low reflectance mode is, the moreadvantageous it is, the upper limit of the reflectance in the highreflection mode state and the lower limit of the reflectance in the lowreflection mode state are not particularly limited, where in oneexample, the reflectance in the high reflection mode state may be about60% or less, 55% or less, or about 50% or less or so, and the lowerlimit of the reflectance in the low reflection mode state may be about0%.

Besides, in one example, in the light modulation device capable ofswitching between the low reflection mode state and the high reflectionmode state, the difference between the reflectance in the highreflection mode state and the reflectance in the low reflection modestate (high reflection mode−low reflection mode) may be 5% or more, 10%or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% ormore, or 40% or more, or may be 90% or less, 85% or less, 80% or less,75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% orless, or 45% or less.

The above-mentioned transmittance and reflectance may be eachtransmittance or reflectance for any one wavelength in the visible lightregion, for example, any one wavelength in a range of about 400 to 700nm or about 380 to 780 nm, or transmittance or reflectance for theentire visible light region, maximum or minimum transmittance orreflectance among the transmittance or reflectance for the entirevisible light region, or an average value of the transmittance or anaverage value of the reflectance in the visible region.

The light modulation device of the present application may be designedto switch between at least two or more states of any one state selectedfrom the transmission mode, the blocking mode, the high reflection modeand the low reflection mode, and another state. If necessary, otherstates other than the above states, for example, other third states orfurther states including an intermediate transmittance state in thetransmission mode and blocking mode states, an intermediate reflectancestate in the high reflection mode and low reflection mode states, or thelike can also be implemented.

The switching of the light modulation device may be controlled dependingon whether or not an external signal, for example, a voltage signal isapplied. For example, in a state of not applying an external signal suchas a voltage, the light modulation device may maintain any one of theabove-described states, and then may be switched to another state when avoltage is applied. The state of the mode may be changed or the thirddifferent mode state may also be implemented, by changing the intensity,frequency and/or shape of the applied voltage.

The light modulation device of the present application may basicallycomprise a light modulation film layer having two substrates disposedopposite to each other and a light modulation layer positioned betweenthe substrates. Hereinafter, for convenience, any one of the twosubstrates disposed opposite to each other will be referred to as afirst substrate, and the other substrate will be referred to as a secondsubstrate.

FIG. 1 is a cross-sectional diagram of an exemplary light modulationfilm layer of the present application, where the light modulation filmlayer may comprise first and second polymer film substrates (11, 13),and a light modulation layer (12) present between the first and secondpolymer film substrates.

In the light modulation device of the present application, a polymerfilm substrate is applied as the substrate. The substrate of the lightmodulation device may not comprise a glass layer. The presentapplication can constitute a device having no optical defect such as aso-called rainbow phenomenon but excellent mechanical properties, bydisposing polymer film substrates having optically large anisotropy andalso anisotropy even in terms of mechanical properties in a specificrelationship. Such a result is contrary to the common sense of the priorart that optically isotropic substrates must be applied in order tosecure excellent optical properties and substrates having isotropicmechanical properties are advantageous in terms of mechanical propertiessuch as dimensional stability of the device.

In this specification, the polymer film substrate having anisotropy interms of optical and mechanical properties may be referred to as anasymmetric substrate or an asymmetric polymer film substrate. Here, thefact that the polymer film substrate is optically anisotropic is thecase of having the above-described in-plane retardation, and the factthat it is anisotropic in terms of mechanical properties is the case ofhaving physical properties to be described below.

Hereinafter, physical properties of the polymer film substrate mentionedherein may be physical properties of the polymer film substrate itself,or physical properties in a state where an electrode layer is formed onone side of the polymer film substrate. In this case, the electrodelayer may be an electrode layer formed in a state where the polymer filmsubstrate is included in the optical device.

Measurement of physical properties of each polymer film substratementioned herein is performed according to the method described in theexample section of this specification.

In one example, the in-plane retardation of the first and second polymerfilm substrates may be about 4,000 nm or more, respectively.

In this specification, the in-plane retardation (Rin) may mean a valuecalculated by Equation 1 below.Rin=d×(nx−ny)  [Equation 1]

In Equation 1, Rin is in-plane retardation, d is a thickness of thepolymer film substrate, nx is a refractive index in the in-plane slowaxis direction of the polymer film substrate, ny is a refractive indexin the fast axis direction, which is the refractive index of thein-plane direction perpendicular to the slow axis direction.

The in-plane retardation of each of the first and second polymer filmsubstrates may be 4,000 nm or more, 5,000 nm or more, 6,000 nm or more,7,000 nm or more, 8,000 nm or more, 9,000 nm or more, 10,000 nm or more,11,000 nm or more, 12,000 nm or more, 13,000 nm or more, 14,000 nm ormore, or 15,000 nm or more or so. The in-plane retardation of each ofthe first and second polymer film substrates may be about 50,000 nm orless, about 40,000 nm or less, about 30,000 nm or less, 20,000 nm orless, 18,000 nm or less, 16,000 nm or less, 15,000 nm or less, or 12,000nm or less or so.

As a polymer film having large retardation as above, a film known as aso-called high-stretched PET (poly(ethylene terephthalate)) film or SRF(super retardation film), and the like is typically known. Therefore, inthe present application, the polymer film substrate may be, for example,a polyester film substrate.

The film having extremely high retardation as above is known in the art,and such a film exhibits high asymmetry even in mechanical properties byhigh stretching or the like during preparation procedures as well asoptically large anisotropy. A representative example of the polymer filmsubstrate in a state known in the art is a polyester film such as a PET(poly(ethylene terephthalate)) film, and for example, there are films ofthe trade name SRF (super retardation film) series supplied by ToyoboCo., Ltd.

Unless otherwise specified, each of the polymer film substrates may havea thickness direction retardation value of about 1,000 nm or less ascalculated by Equation 2 below.Rth=d×(nz−ny)  [Equation 2]

In Equation 2, Rth is thickness direction retardation, d is a thicknessof the polymer film substrate, and ny and nz are refractive indexes inthe y axis and z axis directions of the polymer film substrate,respectively. The y axis of the polymer film substrate is the in-planefast axis direction, and the z axis direction means the thicknessdirection of the polymer film substrate.

The polymer film substrate may also have gas permeability of less than0.002 GPU at room temperature. The gas permeability of the polymer filmsubstrate may be, for example, 0.001 GPU or less, 0.0008 GPU or less,0.006 GPU or less, 0.004 GPU or less, 0.002 GPU or less, or 0.001 GPU orless. When the gas permeability of the polymer film substrate is withinthe above range, it is possible to provide a light modulation devicehaving excellent durability in which void generation by an external gasis suppressed. The lower limit of the range of the gas permeability isnot particularly limited. That is, the gas permeability is moreadvantageous, as the value is smaller.

In one example, in each of the polymer film substrates, a ratio (E1/E2)of an elongation (E1) in any first direction in the plane to anelongation (E2) in a second direction perpendicular to the firstdirection may be 3 or more. In another example, the ratio (E1/E2) may beabout 3.5 or more, 4 or more, 4.5 or more, 5 or more, 5.5 or more, 6 ormore, or 6.5 or more. In another example, the ratio (E1/E2) may be about20 or less, 18 or less, 16 or less, 14 or less, 12 or less, 10 or less,8 or less, or 7.5 or less.

As used herein, the terms “first direction,” “second direction” and“third direction” of the polymer film substrate are each any in-planedirection of the film substrate. For example, when the polymer filmsubstrate is a stretched polymer film substrate, the in-plane directionmay be an in-plane direction formed by MD (machine direction) and TD(transverse direction) directions of the polymer film substrate. In oneexample, the first direction described herein may be any one of the slowaxis direction and the fast axis direction of the polymer filmsubstrate, and the second direction may be the other of the slow axisdirection and the fast axis direction. In another example, when thepolymer film substrate is a stretched polymer film substrate, the firstdirection may be any one of MD (machine direction) and TD (transversedirection) directions, and the second direction may be the other of MD(machine direction) and TD (transverse direction) directions.

In one example, the first direction of the polymer film substratementioned herein may be the TD direction or the slow axis direction.

Each of the first and second polymer film substrates may have theelongation in the first direction of 15% or more, or 20% or more. Inanother example, the elongation may be about 25% or more, 30% or more,35% or more, or 40% or more, or may be about 100% or less, 90% or less,80% or less, 70% or less, about 60% or less, 55% or less, 50% or less,or 45% or less.

In one example, in each of the first and second polymer film substrates,an elongation (E3) in a third direction forming an angle within a rangeof 40 degrees to 50 degrees or about 45 degrees with the first andsecond directions, respectively, is larger than the elongation (E1) inthe first direction (for example, the above-described slow axialdirection or TD direction), where the ratio (E3/E2) of the elongation(E3) in the third direction to the elongation (E2) in the seconddirection may be 5 or more.

In another example, the ratio (E3/E2) may be 5.5 or more, 6 or more, 6.5or more, 7 or more, 7.5 or more, 8 or more, or 8.5 or more, and may beabout 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10or less.

The angle formed by the third direction and the first or seconddirection is an acute angle of the angles formed by the first directionand the third direction, and is an acute angle of the angles formed bythe second direction and the third direction.

Here, each of the first and second polymer film substrates may have theelongation in the third direction of 30% or more. In another example,the elongation may be about 35% or more, 40% or more, 45% or more, 50%or more, or 55% or more, or may be about 80% or less, 75% or less, 70%or less, or 65% or less.

In each of the first and second polymer film substrates, a ratio(CTE2/CTE1) of a coefficient of thermal expansion (CTE2) in the seconddirection to a coefficient of thermal expansion (CTE1) in the firstdirection (for example, the above-described slow axis direction or TDdirection) may be 1.5 or more. The coefficients of thermal expansion(CTE1, CTE2) are each a value confirmed within a temperature range of40° C. to 80° C. In another example, the ratio (CTE2/CTE1) may be about2 or more, about 2.5 or more, 3 or more, or 3.5 or more, or may be 10 orless, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, or 4 orless.

The coefficient of thermal expansion (CTE2) in the second direction maybe in a range of 5 to 150 ppm/° C. The coefficient of thermal expansionmay be about 10 ppm/° C. or more, 15 ppm/° C. or more, 20 ppm/° C. ormore, 25 ppm/° C. or more, 30 ppm/° C. or more, 35 ppm/° C. or more, 40ppm/° C. or more, 45 ppm/° C. or more, 50 ppm/° C. or more, 55 ppm/° C.or more, 60 ppm/° C. or more, 65 ppm/° C. or more, 70 ppm/° C. or more,75 ppm/° C. or more, or 80 ppm/° C. or more, or may be 140 ppm/° C. orless, 130 ppm/° C. or less, 120 ppm/° C. or less, 100 ppm/° C. or less,95 ppm/° C. or less, 90 ppm/° C. or less, 85 ppm/° C. or less, 80 ppm/°C. or less, 40 ppm/° C. or less, 30 ppm/° C. or less, or 25 ppm/° C. orless.

In each of the first and second polymer film substrates, a ratio(YM1/YM2) of an elastic modulus (YM1) in the first direction (forexample, the above-described slow axis direction or TD direction) to anelastic modulus (YM2) in the second direction may be 1.5 or more. Inanother example, the ratio (YM1/YM2) may be about 2 or more, or may be10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 orless, 3 or less or 2.5 or less.

The elastic modulus (YM1) in the first direction (for example, theabove-described slow axis direction or TD direction) may be in a rangeof about 2 to 10 GPa. In another example, the elastic modulus (YM1) maybe about 2.5 GPa or more, 3 GPa or more, 3.5 GPa or more, 4 GPa or more,4.5 GPa or more, 5 GPa or more, or 5.5 GPa or more, or may also be about9.5 GPa or less, 9 GPa or less, 8.5 GPa or less, 8 GPa or less, 7.5 GPaor less, 7 GPa or less, 6.5 GPa or less, or 6 GPa or less.

The elastic modulus is a so-called Young's modulus, which is measuredaccording to the method of the example described below.

In each of the first and second polymer film substrates, a ratio(MS1/MS2) of a maximum stress (MS1) in the first direction (for example,the above-described slow axis direction or TD direction) to a maximumstress (MS2) in the second direction may be 1.5 or more. In anotherexample, the ratio (MS1/MS2) may be about 2 or more, or may be 10 orless, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less,3 or less, or 2.5 or less.

The maximum stress (MS1) in the first direction (for example, theabove-described slow axis direction or TD direction) may be in a rangeof about 80 to 300 MPa. In another example, the maximum stress (MS1) maybe about 90 MPa or more, about 100 MPa or more, about 110 MPa or more,about 120 MPa or more, about 130 MPa or more, about 140 MPa or more,about 150 MPa or more, about 155 MPa or more, 160 MPa or more, 165 MPaor more, 170 MPa or more, 175 MPa or more, or 180 MPa or more, or mayalso be about 300 MPa or less, about 290 MPa or less, about 280 MPa orless, about 270 MPa or less, about 260 MPa or less, about 250 MPa orless, about 245 MPa or less, 240 MPa or less, 235 MPa or less, 230 MPaor less, 225 MPa or less, 220 MPa or less, 215 MPa or less, 210 MPa orless, 205 MPa or less, 200 MPa or less, 195 MPa or less, or 190 MPa orless.

In the light modulation device of the present application, an absolutevalue of the angle formed by the first direction of the first polymerfilm substrate and the first direction of the second polymer filmsubstrate may be in a range of 0 degrees to 10 degrees or 0 degrees to 5degrees, or the first directions may be approximately horizontal to eachother. The first direction may be the slow axis direction or the TDdirection of the polymer film substrate as described above.

As the device is configured by disposing polymer film substrates havingasymmetric optical and mechanical properties so as to have such aspecific relationship as described above, the present application canrealize excellent optical and mechanical properties.

Although the reason why such an effect is realized is not clear, it isassumed that it is because a better balance of optical and mechanicalproperties is secured by controlling the large asymmetry, in which atleast two polymer film substrates have, similarly and again disposingboth asymmetry to be symmetric based on a specific axis, as comparedwith application of a film having an isotropic structure.

The thickness of each of the first and second polymer film substrates isnot particularly limited, which may be set in an appropriate rangedepending on the purpose. Typically, the thickness may be in a range ofabout 10 μm to 200 μm.

As described above, a representative example of the polymer film havinglarge optical and mechanical asymmetry as above is a stretched PET(polyethyleneterephtalate) film known as a so-called high stretchedpolyester film or the like, and such a film is easily available in theindustry.

Usually, the stretched PET film is a uniaxially stretched film of one ormore layers produced by forming a PET-based resin into a film withmelting/extruding, and stretching it or a biaxially stretched film ofone or more layers produced by longitudinally and transverselystretching it after film formation.

The PET-based resin generally means a resin in which 80 mol % or more ofthe repeating units are ethylene terephthalate, which may also containother dicarboxylic acid components and diol components. Otherdicarboxylic acid components are not particularly limited, but mayinclude, for example, isophthalic acid, p-beta-oxyethoxybenzoic acid,4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone,bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid and/or1,4-dicarboxycyclohexane, and the like.

Other diol components are not particularly limited, but may includepropylene glycol, butanediol, neopentyl glycol, diethylene glycol,cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethyleneglycol, polypropylene glycol and/or polytetramethylene glycol, and thelike.

The dicarboxylic acid component or the diol component may be used incombination of two or more as necessary. Furthermore, an oxycarboxylicacid such as p-oxybenzoic acid may also be used in combination. Inaddition, as other copolymerization components, a dicarboxylic acidcomponent containing a small amount of amide bonds, urethane bonds,ether bonds and carbonate bonds, and the like, or a diol component mayalso be used.

As a production method of the PET-based resin, a method of directlypolycondensing terephthalic acid, ethylene glycol and/or, as necessary,other dicarboxylic acids or other diols, a method of transesterifyingdialkyl ester of terephthalic acid and ethylene glycol and/or, asnecessary, dialkyl esters of other dicarboxylic acids or other diols andthen polycondensing them, and a method of polycondensing terephtalicacid and/or, as necessary, ethylene glycol esters of other dicarboxylicacids and/or, as necessary, other diolesters, and the like are adopted.

For each polymerization reaction, a polymerization catalyst containingan antimony-based, titanium-based, germanium-based or aluminum-basedcompound, or a polymerization catalyst containing the composite compoundcan be used.

The polymerization reaction conditions can be appropriately selecteddepending on monomers, catalysts, reaction apparatuses and intendedresin physical properties, and are not particularly limited, but forexample, the reaction temperature is usually about 150° C. to about 300°C., about 200° C. to about 300° C. or about 260° C. to about 300° C.Furthermore, the reaction pressure is usually atmospheric pressure toabout 2.7 Pa, where the pressure may be reduced in the latter half ofthe reaction.

The polymerization reaction proceeds by volatilizing leaving reactantssuch as a diol, an alkyl compound or water.

The polymerization apparatus may also be one which is completed by onereaction tank or connects a plurality of reaction tanks. In this case,the reactants are polymerized while being transferred between thereaction tanks, depending on the degree of polymerization. In addition,a method, in which a horizontal reaction apparatus is provided in thelatter half of the polymerization and the reactants are volatilizedwhile heating/kneading, may also be adopted.

After completion of the polymerization, the resin is discharged from thereaction tank or the horizontal reaction apparatus in a molten state,and then, obtained in the form of flakes cooled and pulverized in acooling drum or a cooling belt, or in the form of pellets tailored afterbeing introduced into an extruder and extruded in a string shape.Furthermore, solid-phase polymerization may be performed as needed,thereby improving the molecular weight or decreasing the low molecularweight component. As the low molecular weight component that may becontained in the PET resin, a cyclic trimer component may beexemplified, but the content of such a cyclic trimer component in theresin is usually controlled to 5,000 ppm or less, or 3,000 ppm or less.

The molecular weight of the PET-based resin is usually in a range of0.45 to 1.0 dL/g, 0.50 to 1.0 dL/g or 0.52 to 0.80 dL/g, when the resinhas been dissolved in a mixed solvent of phenol/tetrachloroethane=50/50(weight ratio) and it has been represented as a limiting viscositymeasured at 30° C.

In addition, the PET-based resin may contain additives as required. Theadditive may include a lubricant, an anti-blocking agent, a heatstabilizer, an antioxidant, an antistatic agent, a light stabilizer andan impact resistance improver, and the like. The addition amount thereofis preferably within a range that does not adversely affect the opticalproperties.

The PET-based resin is used in the form of pellets assembled by anordinary extruder, for formulation of such additives and film molding tobe described below. The size and shape of the pellets are notparticularly limited, but they are generally a cylindrical, spherical orflat spherical shape having both height and diameter of 5 mm or less.The PET-based resin thus obtained can be molded into a film form andsubjected to a stretching treatment to obtain a transparent andhomogeneous PET film having high mechanical strength. The productionmethod thereof is not particularly limited, and for example, thefollowing method is adopted.

Pellets made of the dried PET resin are supplied to a melt extrusionapparatus, heated to a melting point or higher and melted. Next, themelted resin is extruded from the die and quenched and solidified on arotary cooling drum to a temperature below the glass transitiontemperature to obtain an un-stretched film in a substantially amorphousstate. This melting temperature is determined according to the meltingpoint of the PET-based resin to be used or the extruder, which is notparticularly limited, but is usually 250° C. to 350° C. In order toimprove planarity of the film, it is also preferred to enhance adhesionbetween the film and the rotary cooling drum, and an adhesion method byelectrostatic application or an adhesion method by liquid coating ispreferably adopted. The adhesion method by electrostatic application isusually a method in which linear electrodes are provided on the uppersurface side of a film in a direction perpendicular to the flow of thefilm and a direct current voltage of about 5 to 10 kV is applied to theelectrodes to provide static charges to the film, thereby improving theadhesion between the rotary cooling drum and the film. In addition, theadhesion method by liquid coating is a method for improving the adhesionbetween the rotary cooling drum and the film by uniformly coating aliquid to all or a part (for example, only the portion in contact withboth film ends) of the surface of the rotary cooling drum. Both of themmay also be used in combination if necessary. The PET-based resin to beused may be mixed with two or more resins, or resins having differentstructures or compositions, if necessary. For example, it may includeusing a mixture of pellets blended with a particulate filling materialas an anti-blocking agent, an ultraviolet absorbing agent or anantistatic agent, and the like, and non-blended pellets, and the like.

Furthermore, the laminating number of films to be extruded may also betwo or more layers, if necessary. For example, it may include thatpellets blended with a particulate filling material as an anti-blockingagent and non-blended pellets are prepared and supplied from the otherextruder to the same die to extrude a film composed of two kinds andthree layers, “blended with filling material/no-blended/blended withfilling material,” and the like.

The un-stretched film is usually stretched longitudinally at atemperature not lower than the glass transition temperature in theextrusion direction first. The stretching temperature is usually 70 to150° C., 80 to 130° C., or 90 to 120° C. In addition, the stretchingratio is usually 1.1 to 6 times or 2 to 5.5 times. The stretching may beterminated once or divided into more than once as necessary.

The longitudinally stretched film thus obtained may be subjected to aheat treatment thereafter. Then, a relaxation treatment may be performedif necessary. The heat treatment temperature is usually 150 to 250° C.,180 to 245° C. or 200 to 230° C. Also, the heat treatment time isusually 1 to 600 seconds or 1 to 300 seconds or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 90 to 200° C. or120 to 180° C. Also, the amount of relaxation is usually 0.1 to 20% or 2to 5%. The relaxation treatment temperature and the relaxation amountcan be set so that a heat shrinkage rate of the PET film afterrelaxation treatment at 150° C. is 2% or less.

In the case of obtaining uniaxially stretched and biaxially stretchedfilms, transverse stretching is usually performed by a tenter after thelongitudinal stretching treatment or after the heat treatment orrelaxation treatment, if necessary. The stretching temperature isusually 70 to 150° C., 80 to 130° C., or 90 to 120° C. In addition, thestretching ratio is usually 1.1 to 6 times or 2 to 5.5 times.Thereafter, the heat treatment and, if necessary, the relaxationtreatment can be performed. The heat treatment temperature is usually150 to 250° C. or 180 to 245° C. or 200 to 230° C. The heat treatmenttime is usually 1 to 600 seconds, 1 to 300 seconds, or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 100 to 230° C.,110 to 210° C. or 120 to 180° C. Also, the relaxation amount is usually0.1 to 20%, 1 to 10%, or 2 to 5%. The relaxation treatment temperatureand the relaxation amount can be set so that the heat shrinkage rate ofthe PET film after the relaxation treatment at 150° C. is 2% or less.

In uniaxial stretching and biaxial stretching treatments, in order toalleviate deformation of the orientation main axis as represented bybowing, the heat treatment can be performed again or the stretchingtreatment can be performed after the transverse stretching. The maximumvalue of deformation in the orientation main axis by bowing with respectto the stretching direction is usually within 45 degrees, within 30degrees, or within 15 degrees. Here, the stretching direction alsorefers to a stretching large direction in longitudinal stretching ortransverse stretching.

In the biaxial stretching of the PET film, the transverse stretchingratio is usually slightly larger than the longitudinal stretching ratio,where the stretching direction refers to a direction perpendicular tothe long direction of the film. Also, the uniaxial stretching is usuallystretched in the transverse direction as described above, where thestretching direction equally refers to a direction perpendicular to thelong direction.

Also, the orientation main axis refers to a molecular orientationdirection at any point on the stretched PET film. Furthermore, thedeformation of the orientation main axis with respect to the stretchingdirection refers to an angle difference between the orientation mainaxis and the stretching direction. In addition, the maximum valuethereof refers to a maximum value of the values on the verticaldirection with respect to the long direction.

The direction of identifying the orientation main axis is known, and forexample, it can be measured using a retardation film/optical materialinspection apparatus RETS (manufactured by Otsuka Densi KK) or amolecular orientation system MOA (manufactured by Oji ScientificInstruments).

The stretched PET film used in the present application may be impartedwith antiglare properties (haze). The method of imparting antiglareproperties is not particularly limited, and for example, a method ofmixing inorganic particulates or organic particulates into the raw resinto form a film, a method of forming a stretched film from anun-stretched film having a layer, in which inorganic particulates ororganic particulates are mixed, on one side, based on the method ofproducing the film, or a method of coating a coating liquid formed bymixing inorganic particulates or organic particulates with a curablebinder resin on one side of a stretched PET film and curing the binderresin to form an antiglare layer, and the like is adopted.

The inorganic particulates for imparting antiglare properties are notparticularly limited, but may include, for example, silica, colloidalsilica, alumina, alumina sol, an aluminosilicate, an alumina-silicacomposite oxide, kaolin, talc, mica, calcium carbonate, and the like.Also, the organic particulates are not particularly limited, but mayinclude, for example, crosslinked polyacrylic acid particles, methylmethacrylate/styrene copolymer resin particles, crosslinked polystyreneparticles, crosslinked polymethyl methacrylate particles, silicone resinparticles and polyimide particles, and the like. The antiglareproperty-imparted stretched PET film thus obtained may have a haze valuein a range of 6 to 45%.

A functional layer such as a conductive layer, a hard coating layer anda low reflective layer may be further laminated on the antiglareproperty-imparted stretched PET film. Furthermore, as the resincomposition constituting the antiglare layer, a resin composition havingany one of these functions may also be selected.

The haze value can be measured using, for example, a haze-permeabilitymeter HM-150 (manufactured by Murakami Color Research Laboratory, Co.,Ltd.) in accordance with JIS K 7136. In the measurement of the hazevalue, in order to prevent the film from being warped, for example, ameasurement sample in which the film surface is bonded to a glasssubstrate using an optically transparent pressure-sensitive adhesive sothat the antiglare property-imparted surface becomes the surface can beused.

The functional layer other than the antiglare layer or the like can belaminated on one side or both sides of the stretched PET film used inthe present application, unless it interferes with the effect of thepresent application. The functional layer to be laminated may include,for example, a conductive layer, a hard coating layer, a smoothinglayer, an easily slipping layer, an anti-blocking layer and an easyadhesion layer, and the like.

The above-described method for producing a PET film is one exemplarymethod for obtaining the polymer film substrate of the presentapplication, where as long as the polymer film substrate applicable inthe present application has the above-described physical properties, anykind of commercially available product can also be used.

In one example, the polymer film substrate may be a film substrate thatan electrode layer is formed on one side. Such a film substrate may bereferred to as an electrode film substrate. The above-mentionedretardation or mechanical properties, and the like may be for thepolymer film substrate on which the electrode layer is not formed, orfor the electrode film substrate.

In the case of the electrode film substrate, each of electrode layersmay be formed on at least one side of the polymer film substrate, andfirst and second polymer film substrates may be disposed so that theelectrode layers face each other.

As the electrode layer, a known transparent electrode layer may beapplied, and for example, a so-called conductive polymer layer, aconductive metal layer, a conductive nanowire layer, or a metal oxidelayer such as ITO (indium tin oxide) may be used as the electrode layer.Besides, various materials and forming methods capable of forming atransparent electrode layer are known, which can be applied withoutlimitation.

In addition, an alignment film may be formed on one side of the polymerfilm substrate, for example, the upper part of the electrode layer inthe case of the electrode film substrate. A known liquid crystalalignment film can be formed as the alignment film, and the kind ofalignment film that can be applied according to a desired mode is known.

As described above, in the present application, the light modulationlayer included in the light modulation film layer is a functional layercapable of changing the transmittance, reflectivity and/or haze of lightdepending on whether or not an external signal is applied. Such a lightmodulation layer in which the state of light changes depending onwhether or not an external signal is applied, or the like, can bereferred to as an active light modulation layer herein. In one example,when the light modulation layer is a layer containing a liquid crystalcompound, the light modulation layer may be referred to as an activeliquid crystal layer, where the active liquid crystal layer means aliquid crystal layer in a form that the liquid crystal compound can bechanged in the active liquid crystal layer by application of theexternal signal. Also, the light modulation film layer comprising theactive liquid crystal layer may be referred to as an active liquidcrystal film layer.

The external signal herein may mean any external factors, such as anexternal voltage, that may affect the behavior of a material containedin the light modulation layer, for example, a light modulating material.Therefore, the state without external signal may mean a state where noexternal voltage or the like is applied.

In the present application, the type of the light modulation layer isnot particularly limited as long as it has the above-describedfunctions, and a known light modulation layer can be applied. In oneexample, the light modulation layer may be a liquid crystal layer, and astructure including a liquid crystal layer between the first and secondpolymer film substrates arranged opposite to each other may also bereferred to as a liquid crystal cell herein.

An exemplary light modulation device can have excellent durabilityagainst gas permeability. In one example, the light modulation devicemay have a void generation rate of 20% or less upon being stored at atemperature of 60° C. and 85% relative humidity. The void generationrate may mean a percentage of the number of void generation samplesrelative to the number of samples used in the void generationevaluation. In another example, the first and second polymer filmsubstrates may be substrates heat-treated at a temperature of 130° C.for 1 hour, where the light modulation device comprising such polymerfilm substrates may not cause voids due to the inflow of external gasfor 500 hours when stored at a temperature of 60° C. and 85% relativehumidity. This can be achieved by disposing the transverse directions ofthe first and second polymer film substrates so as to be parallel toeach other, as described above.

In one example, the light modulation layer may be an active liquidcrystal layer comprising liquid crystal molecules (liquid crystal host)and dichroic dyes. Such a liquid crystal layer may be referred to as aguest host liquid crystal layer (GHLC layer). In this case, thestructure comprising the light modulation layer between the polymer filmsubstrates may be referred to as an active liquid crystal film layer. Inthis specification, the term “GHLC layer” may mean a layer that dichroicdyes may be arranged together depending on arrangement of liquid crystalmolecules to exhibit anisotropic light absorption characteristics withrespect to an alignment direction of the dichroic dyes and the directionperpendicular to the alignment direction, respectively. For example, thedichroic dye is a substance whose absorption rate of light varies with apolarization direction, where if the absorption rate of light polarizedin the long axis direction is large, it may be referred to as a p-typedye, and if the absorption rate of polarized light in the short axisdirection is large, it may be referred to as an n-type dye. In oneexample, when a p-type dye is used, the polarized light vibrating in thelong axis direction of the dye may be absorbed and the polarized lightvibrating in the short axis direction of the dye may be less absorbed tobe transmitted. Hereinafter, unless otherwise specified, the dichroicdye is assumed to be a p-type dye, but the type of the dichroic dyeapplied in the present application is not limited thereto.

In one example, the GHLC layer may function as an active polarizer. Inthis specification, the term “active polarizer” may mean a functionalelement capable of controlling anisotropic light absorption depending onapplication of external action. For example, the active GHLG layer cancontrol the anisotropic light absorption for the polarized light in thedirection parallel to the arrangement direction of dichroic dyes and thepolarized light in the vertical direction by controlling the arrangementof liquid crystal molecules and dichroic dyes. Since the arrangement ofliquid crystal molecules and dichroic dyes can be controlled by theapplication of external action such as a magnetic field or an electricfield, the active GHLC layer can control anisotropic light absorptiondepending on the application of external action.

The kind and physical properties of the liquid crystal molecules can beappropriately selected in consideration of the object of the presentapplication.

In one example, the liquid crystal molecules may be nematic liquidcrystals or smectic liquid crystals. The nematic liquid crystals maymean liquid crystals in which rod-like liquid crystal molecules have noregularity about positions but are arranged in parallel to the long axisdirection of the liquid crystal molecules, and the smectic liquidcrystals may mean liquid crystals in which rod-like liquid crystalmolecules are regularly arranged to form a layered structure and arealigned in parallel with the regularity in the long axis direction.According to one example of the present application, nematic liquidcrystals may be used as the liquid crystal molecules.

In one example, the liquid crystal molecules may be non-reactive liquidcrystal molecules. The non-reactive liquid crystal molecules may meanliquid crystal molecules having no polymerizable group. Here, thepolymerizable group may be exemplified by an acryloyl group, anacryloyloxy group, a methacryloyl group, a methacryloyloxy group, acarboxyl group, a hydroxyl group, a vinyl group or an epoxy group, andthe like, but is not limited thereto, and a known functional group knownas the polymerizable group may be included.

The refractive index anisotropy of the liquid crystal molecules can beappropriately selected in consideration of target physical properties,for example, variable transmittance characteristics. In thisspecification, the term “refractive index anisotropy” may mean adifference between an extraordinary refractive index and an ordinaryrefractive index of liquid crystal molecules. The refractive indexanisotropy of the liquid crystal molecules may be, for example, 0.01 to0.3. The refractive index anisotropy may be 0.01 or more, 0.05 or more,0.07 or more, 0.09 or more, or 0.1 or more, and may be 0.3 or less, 0.2or less, 0.15 or less, 0.14 or less, or 0.13 or less. When therefractive index anisotropy of the liquid crystal molecules is withinthe above range, it is possible to provide a light modulation devicehaving excellent variable transmittance characteristics. In one example,the lower the refractive index of the liquid crystal molecules is in theabove range, the light modulation device having more excellent variabletransmittance characteristics can be provided.

The dielectric constant anisotropy of the liquid crystal molecules mayhave positive dielectric constant anisotropy or negative dielectricconstant anisotropy in consideration of a driving method of a targetliquid crystal cell. In this specification, the term “dielectricconstant anisotropy” may mean a difference between an extraordinarydielectric constant (εe) and an ordinary dielectric constant (εo) of theliquid crystal molecules. The dielectric constant anisotropy of theliquid crystal molecules may be, for example, in a range within ±40,within ±30, within ±10, within ±7, within ±5 or within ±3. When thedielectric constant anisotropy of the liquid crystal molecules iscontrolled within the above range, it may be advantageous in terms ofdriving efficiency of the light modulation element.

The liquid crystal layer may comprise a dichroic dye. The dye may beincluded as a guest material. The dichroic dye may serve, for example,to control the transmittance of the light modulation device depending onorientation of a host material. In this specification, the term “dye”may mean a material capable of intensively absorbing and/or deforminglight in at least a part or all of the ranges within a visible lightregion, for example, within a wavelength range of 400 nm to 700 nm, andthe term “dichroic dye” may mean a material capable of anisotropicabsorption of light in at least a part or all of the ranges of thevisible light region.

As the dichroic dye, for example, a known dye known to have propertiesthat can be aligned depending on the alignment state of the liquidcrystal molecules by a so-called host guest effect can be selected andused. An example of such a dichroic dye includes a so-called azo dye, ananthraquinone dye, a methine dye, an azomethine dye, a merocyanine dye,a naphthoquinone dye, a tetrazine dye, a phenylene dye, a quaterrylenedye, a benzothiadiazole dye, a diketopyrrolopyrrole dye, a squaraine dyeor a pyromethene dye, and the like, but the dye applicable in thepresent application is not limited thereto. Such a dye is known, forexample, as an azo dye or an anthraquinone dye, and the like, but is notlimited thereto.

As the dichroic dye, a dye having a dichroic ratio, that is, a valueobtained by dividing the absorption of the polarized light parallel tothe long axis direction of the dichroic dye by the absorption of thepolarized light parallel to the direction perpendicular to the long axisdirection, of 5 or more, 6 or more, or 7 or more, can be used. The dyemay satisfy the dichroic ratio in at least a part of the wavelengths orany one wavelength within the wavelength range of the visible lightregion, for example, within the wavelength range of about 380 nm to 700nm or about 400 nm to 700 nm. The upper limit of the dichroic ratio maybe, for example, 20 or less, 18 or less, 16 or less, or 14 or less orso.

The content of the dichroic dye in the liquid crystal layer can beappropriately selected in consideration of the object of the presentapplication. For example, the content of the dichroic dye in the liquidcrystal layer may be 0.1 wt % or more, 0.25 wt % or more, 0.5 wt % ormore, 0.75 wt % or more, 1 wt % or more, 1.25 wt % or more, or 1.5 wt %or more. The upper limit of the content of the dichroic dye in theliquid crystal layer may be, for example, 5.0 wt % or less, 4.0 wt % orless, 3.0 wt % or less, 2.75 wt % or less, 2.5 wt % or less, 2.25 wt %or less, 2.0 wt % or less, 1.75 wt % or less, or 1.5 wt % or less. Whenthe content of the dichroic dye in the liquid crystal layer satisfiesthe above range, it is possible to provide a light modulation devicehaving excellent variable transmittance characteristics. In one example,the higher the content of the dichroic dye is in the above range, thelight modulation device having more excellent variable transmittancecharacteristic can be provided.

In the liquid crystal layer, the total weight of the liquid crystalmolecules and the dichroic dye may be, for example, about 60 wt % ormore, 65 wt % or more, 70 wt % or more, 75 wt % or more, 80 wt % ormore, 85 wt % or more, 90 wt % or more, or 95 wt % or more, and inanother example, it may be less than about 100 wt %, 98 wt % or less, or96 wt % or less.

The liquid crystal layer can switch the orientation state depending onwhether or not a voltage is applied. The voltage may be applied to adirection vertical to the polymer film substrate.

In one example, the liquid crystal layer can be designed to switchbetween a vertical orientation state and a twisting orientation state.Here, the twisting orientation state may be a so-called horizontaltwisting orientation. At this time, the horizontal twisting orientationis a state in which the direction axis of the liquid crystal moleculesis twisted in a horizontal state, which may be for example, the casewhere a helix axis of the twisting orientation is substantially parallelto the thickness direction of the liquid crystal layer, as describedbelow.

In one example, the liquid crystal layer may be present in a twistingorientation state when no voltage is applied, and may be present in avertical orientation state when a voltage is applied. In the twistingorientation state, the twisted angle may be, for example, in a range ofmore than 0 degrees to 360 degrees or less.

For example, if the twisted angle is about 90 degrees or less in therange, this mode may be referred to as a TN (twisted nematic) mode.According to one example of the present application, in the TN mode, thetwisted angle may be about 10 degrees or more, about 20 degrees or more,about 30 degrees or more, about 40 degrees or more, about 50 degrees ormore, about 60 degrees or more, about 70 degrees or more, about 80degrees or more, or about 90 degrees or so.

In another example, the twisted angle may also be more than about 90degrees in the range, and in this case, this mode may be referred to asa STN (super twisted nematic) mode. According to one example of thepresent application, in the STN mode, the twisted angle may be about 100degrees or more, about 110 degrees or more, about 120 degrees or more,about 130 degrees or more, about 140 degrees or more, about 150 degreesor more, about 160 degrees or more, about 170 degrees or more, about 180degrees or more, about 190 degrees or more, about 200 degrees or more,about 210 degrees or more, about 220 degrees or more, about 230 degreesor more, about 240 degrees or more, about 250 degrees or more, about 260degrees or more, about 270 degrees or more, about 280 degrees or more,about 290 degrees or more, about 300 degrees or more, about 310 degreesor more, about 320 degrees or more, about 330 degrees or more, about 340degrees or more, or about 350 degrees or more, or may be about 270degrees, or about 360 degrees.

In the liquid crystal layer of the twisting orientation, the liquidcrystal molecules may have a spiral structure in which the light axesare oriented in layers while being twisted along a virtual helix axis.The light axis of the liquid crystal molecule may mean the slow axis ofthe liquid crystal molecule, where the slow axis of the liquid crystalmolecule may be parallel to the long axis of the rod-shaped liquidcrystal molecule. The helix axis may be formed to be parallel to thethickness direction of the liquid crystal layer. In this specification,the thickness direction of the liquid crystal layer may mean a directionparallel to a virtual line connecting the lowermost portion and theuppermost portion of the liquid crystal layer at the shortest distance.In one example, the thickness direction of the liquid crystal layer maybe a direction parallel to a virtual line formed in a directionperpendicular to the surface of the polymer substrate. In thisspecification, the twisted angle means an angle formed by the light axisof the liquid crystal molecule existing at the lowermost portion of thetwisting orientation liquid crystal layer and the light axis of theliquid crystal molecule existing at the uppermost portion.

The liquid crystal molecules in the vertically oriented liquid crystallayer may be present in a state where the light axes are arrangedperpendicular to the plane of the liquid crystal layer. For example, thelight axes of the liquid crystal molecules may form an angle of about 70to 90 degrees, 75 to 90 degrees, 80 to 90 degrees or 85 to 90 degrees,preferably 90 degrees with respect to the plane of the liquid crystallayer. The light axes of the plurality of liquid crystal molecules inthe vertically oriented liquid crystal layer may be parallel to eachother and may form an angle in the range of, for example, 0 to 10degrees or 0 to 5 degrees, or of about 0 degrees.

The ratio (d/p) of the thickness (d) and the pitch (p) of the liquidcrystal layer in the twisting orientation liquid crystal layer may be 1or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 orless, 0.4 or less, 0.3 or less, or 0.2 or less. If the ratio (d/p) isout of the range, for example, more than 1, finger domains may occur.The ratio (d/p) may be, for example, more than 0, 0.1 or more, 0.2 ormore, 0.3 or more, 0.4 or more, or 0.5 or more. Here, the thickness (d)of the liquid crystal layer may be synonymous with the cell gap of theliquid crystal cell.

The pitch (p) of the twisting orientation liquid crystal layer may bemeasured by a measuring method using a wedge cell, and specifically, itmay be measured by a method described in Simple method for accuratemeasurement of the cholesteric pitch using a “stripe-wedgeGrandjean-Cano cell of D. Podolskyy, et al. (Liquid Crystals, Vol. 35,No. 7, July 2008, 789-791).

The liquid crystal layer may further comprise a chiral dopant fortwisting orientation. The chiral agent that can be included in theliquid crystal layer can be used without particular limitation as longas it can induce a desired rotation without deteriorating the liquidcrystallinity, for example, the nematic regularity. The chiral agent forinducing rotation in the liquid crystal molecules needs to include atleast chirality in the molecular structure. The chiral agent may beexemplified by, for example, a compound having one or two or moreasymmetric carbons, a compound having an asymmetric point on aheteroatom, such as a chiral amine or a chiral sulfoxide, or a compoundhaving axially asymmetric and optically active sites such as cumulene orbinaphthol. The chiral agent may be, for example, a low molecular weightcompound having a molecular weight of 1,500 or less. As the chiralagent, commercially available chiral nematic liquid crystals, forexample, chiral dopant liquid crystal S-811 available from Merck Co.,Ltd. or LC756 available from BASF may also be used.

The application ratio of the chiral dopant is selected so as to achievethe above ratio (d/p), which is not particularly limited. In general,the content (wt %) of the chiral dopant is calculated by an equation of100/HTP (helical twisting power)×pitch (nm), and an appropriate ratiocan be selected in consideration of the desired pitch with reference tothis method.

The thickness of the liquid crystal layer may be appropriately selectedin consideration of the object of the present application. The thicknessof the liquid crystal layer may be, for example, about 0.01 μm or more,0.1 μm or more, 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more,5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or10 μm or more. The upper limit of the thickness of the liquid crystallayer may be, for example, about 30 μm or less, 25 μm or less, 20 μm orless, or 15 μm or less. When the thickness of the liquid crystal layersatisfies the above range, it is possible to provide a light modulationdevice having excellent variable transmittance characteristics. In oneexample, the thinner the thickness of the liquid crystal layer is in theabove range, the light modulation device having more excellent variabletransmittance characteristics can be provided.

The light modulation device may further comprise first and secondalignment films present inside the first and second polymer filmsubstrates, respectively, as the above-described alignment film. In thisspecification, the inside of the first and second polymer filmsubstrates may mean a side where the light modulation layer is present,and the outside may mean the opposite side to the side where the lightmodulation layer is present.

As the first and second alignment films, a horizontal alignment film ora vertical alignment film may be applied. In one example, the first andsecond alignment films may all be horizontal alignment films. In anotherexample, any one of the first and second alignment films may be ahorizontal alignment film and the other may be a vertical alignmentfilm. According to the light modulation element of the presentapplication, when a horizontal alignment film and a vertical alignmentfilm are applied to the first and second alignment films, respectively,the driving voltage characteristic can be improved as compared with acase where a horizontal alignment film is applied to each of the firstand second alignment films.

The light modulation device can adjust the transmittance, reflectanceand haze by adjusting the orientation state of the liquid crystal layeraccording to whether or not a voltage is applied. The orientation stateof the liquid crystal layer can be controlled by a pretilt of thealignment film.

In this specification, the pretilt may have an angle and a direction.The pretilt angle may be referred to as a polar angle, and the pre-tiltdirection may also be referred to as an azimuthal angle.

The pretilt angle may mean an angle in which the light axis of theliquid crystal molecule forms with respect to a horizontal plane of thealignment film. In one example, the vertical alignment film may have apretilt angle of about 70 degrees to 90 degrees, 75 degrees to 90degrees, 80 degrees to 90 degrees, or 85 degrees to 90 degrees. In oneexample, the pretilt angle of the horizontal alignment film may be about0 to 20 degrees, 0 to 15 degrees, 0 to 10 degrees, or 0 to 5 degrees.

The pretilt direction may mean a direction in which the light axis ofthe liquid crystal molecule is projected on a horizontal plane of thealignment film. The pretilt direction may be an angle formed by theprojected direction and the horizontal axis (WA) of the liquid crystallayer. In this specification, the horizontal axis (WA) of the liquidcrystal layer may mean a direction parallel to the long axis directionof the liquid crystal layer, or a direction parallel to the lineconnecting both eyes of an observer wearing eyewear or an observerobserving a display device when a light modulation element is applied tothe eyewear or the display device such as a TV.

The pretilt directions of the first alignment film and the secondalignment film can be appropriately adjusted in consideration of theorientation of the liquid crystal layer. In one example, the pretiltdirections of the first alignment film and the second alignment film mayform 90 degrees to each other for twisting orientation having a twistedangle of 90 degrees. When the pretilt directions of the first alignmentfilm and the second alignment film are parallel to each other, thepretilt directions of the first alignment film and the second alignmentfilm may be anti-parallel to each other, and for example, may form 170degrees to 190 degrees, 175 degrees to 185 degrees, preferably 180degrees to each other.

The alignment film can be selected and used without particularlimitation as long as it has orientation ability with respect toadjacent liquid crystal layers. As the alignment film, for example, acontact type alignment film such as a rubbing alignment film or a photoalignment film known to be capable of exhibiting orientation propertiesby a non-contact method such as irradiation of linearly polarized lightby including a photo alignment film compound can be used.

It is known to adjust the pretilt direction and angle of the rubbingalignment film or the photo alignment film. In the case of the rubbingalignment film, the pretilt direction can be parallel to the rubbingdirection, and the pretilt angle can be achieved by controlling therubbing conditions, for example, the pressure condition upon rubbing,the rubbing intensity, and the like. In the case of the photo alignmentfilm, the pretilt direction can be controlled by the direction ofpolarized light to be irradiated and the like, and the pretilt angle canbe controlled by the angle of light irradiation, the intensity of lightirradiation, and the like.

In one example, each of the first and second alignment films may be arubbing alignment film. When the rubbing directions of the first andsecond alignment films are disposed to be parallel to each other, therubbing directions of the first and second alignment films may beanti-parallel to each other, and for example, may form 170 degrees to190 degrees, 175 degrees to 185 degrees, or 180 degrees to each other.The rubbing direction can be confirmed by measuring the pretilt angle,and since the liquid crystals generally lie along the rubbing directionand simultaneously generate the pretilt angle, it is possible to measurethe rubbing direction by measuring the pretilt angle. In one example,the transverse directions of the first and second polymer filmsubstrates may each be parallel to the rubbing axis of any one of thefirst and second alignment films.

The light modulation device may further comprise, as the above-describedelectrode layers, first and second electrode layers present inside thefirst and second polymer film substrates, respectively. When the lightmodulation device comprises the first and second alignment films, thefirst electrode layer may exist between the first polymer film substrateand the first alignment film, and the second electrode layer may existbetween the second polymer film substrate and the second alignment film.

The light modulation element may further comprise an antireflectivelayer. In one example, the light modulation element may further comprisefirst and/or second antireflective layers present outside the firstand/or second polymer film substrates, respectively. As theantireflective layer, a known antireflective layer may be used inconsideration of the object of the present application, and for example,an acrylate layer may be used. The antireflective layer may have athickness of, for example, 200 nm or less, or 100 nm or less.

The light modulation element may further comprise an ultravioletabsorbing layer. In one example, the light modulation element mayfurther comprise first and second ultraviolet absorbing layers presentoutside the first and second polymer film substrates, respectively. Asthe ultraviolet absorbing layer, a known ultraviolet absorbing layer maybe suitably selected and used in consideration of the object of thepresent application.

In one example, the light modulation device can be formed by directlycoating the antireflective layer, the ultraviolet absorbing layer, andthe like on the polymer film substrate. If the first and second polymerfilm substrates are used, it may be advantageous in terms of refractiveindex matching and coating process optimization. In this case, there areadvantages that the process can be simplified and the thickness of theelement can be reduced. In another example, in the light modulationdevice, the antireflective layer or the ultraviolet absorbing layer maybe formed on one side of a base film, and the base film may be attachedto the polymer film substrate via a pressure-sensitive adhesive or anadhesive.

The light modulation device may exhibit variable transmittancecharacteristics according to the orientation state of the liquid crystallayer depending on whether or not a voltage is applied. In one example,the light modulation device can switch between the transmission modestate and the blocking mode state as described above.

The light modulation device may be in the blocking state indicating theminimum transmittance when a voltage is not applied to the liquidcrystal layer and may be in the transmission state indicating themaximum transmittance when a voltage is applied.

The light modulation device can be applied to various applications inwhich variable transmittance characteristics are required. Theapplications in which variable transmittance characteristics arerequired can be exemplified by openings in enclosed spaces includingbuildings, containers or vehicles, and the like, such as windows orsunroofs, or eyewear, and the like. Here, in the range of eyewear, alleyewear formed so that an observer can observe the outside throughlenses, such as general glasses, sunglasses, sports goggles or helmets,or instruments for experiencing augmented reality, can be included.

A typical application to which the light modulation device of thepresent application can be applied is eyewear. Recently, sunglasses,sports goggles, augmented reality experience devices, and the like arecommercially available as eyewear in the form in which lenses aremounted so as to be inclined to an observer's frontal line of sight. Thelight modulation device of the present application can be effectivelyapplied to the above-described eyewear.

When the light modulation device of the present application is appliedto eyewear, the structure of the eyewear is not particularly limited.That is, the light modulation device may be mounted and applied in alens for a left eye and/or a right eye having a known eyewear structure.

For example, the eyewear may comprise a left eye lens and a right eyelens; and a frame for supporting the left eye lens and the right eyelens.

FIG. 2 is an exemplary schematic diagram of the eyewear, which is aschematic diagram of the eyewear comprising the frame (82) and the leftand right eye lenses (84), but the eyewear structure to which the lightmodulation device of the present application can be applied is notlimited to the drawing.

In the eyewear, the left eye lens and the right eye lens may eachcomprise the light modulation device. Such a lens may comprise only thelight modulation device, or may also comprise other configurations.

Other configurations and designs of the eyewear are not particularlylimited, and known methods can be applied.

Advantageous Effects

The present application can provide a light modulation device bothexcellent mechanical properties and optical properties by applying anoptically and mechanically anisotropic polymer film as a substrate.

MODE FOR INVENTION

Hereinafter, the present application will be specifically described byway of Examples, but the scope of the present application is not limitedby the following examples.

The polymer film substrates used in Examples or Comparative Examples area PC (polycarbonate) film substrate (PC substrate, thickness: 100 μm,manufacturer: Teijin, product name: PFC100-D150), which is an isotropicfilm substrate usually applied as a substrate, and a PET (polyethyleneterephthalate) film substrate (SRF substrate, thickness: 80 μm,manufacturer: Toyobo, product name: TA044), which is an asymmetricsubstrate according to the present application, and the followingphysical properties are the results of measurement in a state where anITO (indium tin oxide) film having a thickness of about 20 nm is formedon one side of each film substrate.

1. Phase Retardation Evaluation of Polymer Film Substrate

The in-plane retardation value (Rin) of the polymer film substrate wasmeasured for light having a wavelength of 550 nm using a UV/VISspectroscope 8453 instrument from Agilent Co., Ltd. according to thefollowing method. Two sheets of polarizers were installed in the UV/VISspectroscope so that their transmission axes were orthogonal to eachother, and a polymer film was installed between the two sheets ofpolarizers so that its slow axis formed 45 degrees with the transmissionaxes of the two polarizers, respectively, and then the transmittanceaccording to wavelengths was measured. The phase retardation order ofeach peak is obtained from the transmittance graph according towavelengths. Specifically, a waveform in the transmittance graphaccording to wavelengths satisfies Equation A below, and the maximumpeak (Tmax) condition in the sine waveform satisfies Equation B below.In the case of λmax in Equation A, since the T of Equation A and the Tof Equation B are the same, the equations are expanded. As the equationsare also expanded for n+1, n+2 and n+3, arranged for n and n+1 equationsto eliminate R, and arranged for n into λn and λn+1 equations, thefollowing Equation C is derived. Since n and λ can be known based on thefact that T of Equation A and T of Equation B are the same, R for eachof λn, λn+1, λn+2 and λn+3 is obtained. A linear trend line of R valuesaccording to wavelengths for 4 points is obtained and the R value forthe equation 550 nm is calculated. The function of the linear trend lineis Y=ax+b, where a and b are constants. The Y value when 550 nm has beensubstituted for x of the function is the Rin value for light having awavelength of 550 nm.T=sin²[(2πR/λ)]  [Equation A]T=sin²[((2n+1)π/2)]  [Equation B]n=(λn−3λn+1)/(2λn+1+1−2λn)  [Equation C]

In the above, R denotes in-plane retardation (Rin), λ denotes awavelength, and n denotes a nodal degree of a sine waveform.

2. Evaluation of Tensile Property and Coefficient of Thermal Expansionof Polymer Film Substrate

A tensile strength test was conducted according to the standard byapplying a force at a tensile speed of 10 mm/min at room temperature(25° C.) using UTM (Universal Testing Machine) equipment (Instron 3342)to measure the elastic modulus (Young's modulus), elongation and maximumstress of the polymer film substrate. In this case, each specimen wasprepared by tailoring it to have a width of about 10 mm and a length ofabout 30 mm, and both ends in the longitudinal direction were each tapedby 10 mm and fixed to the equipment, and then the evaluation wasperformed.

A length expansion test was conducted according to the standard whileelevating the temperature from 40° C. to 80° C. at a rate of 10° C./minusing TMA (thermomechanical analysis) equipment (Metteler toledo,SDTA840) to measure the coefficient of thermal expansion. Upon themeasurement, the measurement direction length of the specimen was set to10 mm and the load was set to 0.02 N.

The evaluation results of physical properties of each film substratemeasured in the above manner are shown in Table 1 below.

In Table 1 below, MD and TD are MD (machine direction) and TD(transverse direction) directions of the PC substrate and the SRFsubstrate which are stretched films, respectively, and 45 is thedirection forming 45 degrees with both the MD and TD directions.

TABLE 1 Maxi- Coefficient Elastic Elong- mum of Thermal Rin modulusation Stress Expansion Direction (nm) (GPa) (%) (MPa) (ppm/° C.) PC MD12.1 1.6 13.6 63.4 119.19 Substrate TD 1.6 11.6 62.3 127.8 SRF MD 148002.5 6.1 81.5 83.3 Substrate 45 15176 3.2 60.4 101.6 52.2 TD 15049 5.844.7 184.6 21.6

EXAMPLE 1

Two SRF substrates were used to manufacture a light modulation device.An alignment film was formed on an ITO (indium tin oxide) electrodelayer of the SRF substrate (width: 15 cm, length: 5 cm) to prepare afirst substrate. As the alignment film, one obtained by rubbing apolyimide-based horizontal alignment film (SE-7492, Nissan) having athickness of 300 nm with a rubbing cloth was used. A second substratewas prepared in the same manner as the first substrate. The first andsecond substrates were disposed opposite to each other so that theiralignment films faced each other, a mixture, in which a known chiraldopant (S811, Merck) was added to a GHLC mixture (MDA-16-1235, Merck)comprising a liquid crystal compound having positive dielectric constantanisotropy with refractive index anisotropy (ΔN) of 0.13 and a dichroicdye, was positioned therebetween, and then the frame was sealed toprepare a light modulation device. Here, the TD directions (slow axisdirections) of the first and second substrates were each 0 degrees basedon the rubbing axis of the first substrate alignment film, and therubbing directions of the first and second alignment films weresubstantially perpendicular to each other. The obtained light modulationlayer was a TN mode guest host liquid crystal layer, and the cell gapwas 12 μm. Also, the ratio (d/p) of the cell gap (d) to the pitch (p) inthe TN mode was about 0.17.

COMPARATIVE EXAMPLE 1

A light modulation device was manufactured in the same manner as inExample 1, except that a PC substrate was applied as a substrate.

TEST EXAMPLE 1

Using the light modulation devices of Example 1 and Comparative Example1, an eyewear element of the type shown in FIGS. 3 and 4 wasmanufactured, and a heat shock test was conducted in a state of bendingthe element. The heat shock test was performed by setting a step ofraising the temperature of the eyewear from about −40° C. to 90° C. at atemperature increase rate of about 16.25° C./min and then maintaining itfor 10 minutes, and again reducing the temperature from 90° C. to −40°C. at a temperature decrease rate of about 16.25° C./min and thenmaintaining it for 10 minutes as one cycle and repeating the cycle 500times, where this test was conducted with the eyewear attached to abending jig having a curvature radius of about 100R. FIG. 3 showed thecase of Example 1 and FIG. 4 showed the case of Comparative Example 1,where in the case of Comparative Example 1, severe cracks were observedas in the drawing.

COMPARATIVE EXAMPLE 2

A light modulation device was manufactured in the same manner as inExample 1, except that the first directions (TD directions) of the firstand second substrates were set to 90 degrees to each other. At thistime, based on the rubbing direction of the alignment film on the firstsubstrate, the first direction of the first substrate was 0 degrees andthe first direction of the second substrate was 90 degrees.

COMPARATIVE EXAMPLE 3

A light modulation device was manufactured in the same manner as inExample 1, except that the first directions (TD directions) of the firstand second substrates were set to 90 degrees to each other. At thistime, based on the rubbing direction of the alignment film on the firstsubstrate, the first direction of the first substrate was 45 degrees andthe first direction of the second substrate was 135 degrees.

TEST EXAMPLE 2

The void generation was evaluated while the devices of Example 1,Comparative Examples 2 and 3 were each stored at 60° C. and 85% relativehumidity, and the results were shown in Table 2 below. Specifically, itwas evaluated whether or not the visually observed voids occurred in thelight modulation layer while being kept under the above conditions.Generally, the size of the visually observed voids is about 10 μm.

TABLE 2 Number of Number Number First samples of of good occurrenceinitially bad void void Void time introduced samples samples incidenceof void Comparative 2 12 12 0 100% 120 h Example 3 12 12 0 100% 144 hExample 1 12 1 11  8% 504 h

As results of Table 2, in the case of Comparative Examples 2 and 3,voids were observed within 500 hours in all of the initially introducedsamples to show the void incidence of 100%, and the times when the voidswere first observed were also within 120 hours and 144 hours,respectively.

On the other hand, in the case of Example 1, voids were not observedwithin 500 hours, and the time when the voids were first observed wasalso about 504 hours.

TEST EXAMPLE 3

An electro-optical characteristic and occurrence of a rainbow phenomenonwere evaluated for the light modulation device manufactured inExample 1. The electro-optical characteristic was evaluated for thelight modulation device by measuring a change in transmittance dependingon whether or not a voltage was applied. Specifically, the transmittanceaccording to the applied voltage was measured using a haze meter(NDH5000SP, manufactured by Secos) while an AC power was connected tothe electrode layers (ITO layers) of the first and second substrates anddriven. The transmittance is an average of transmittance for lighthaving a wavelength of 380 nm to 780 nm.

The evaluation of the rainbow phenomenon is a cognitive evaluation, andit has been evaluated that the rainbow phenomenon occurs when two ormore patterns representing different luminance rather than the sameluminance in the sample are generated.

In the following evaluation example, “0V_T” is the transmittance uponapplying no voltage, “15V_T” is the transmittance upon applying avoltage of 15V, and “ΔT” is a value of “15V_T”-“0V_T.”

The electro-optical characteristic and the occurrence of the rainbowphenomenon were evaluated for Example 1, and the results were describedin Table 3 below.

TABLE 3 Example 1 Cell Gap 12 μm Δn 0.13 Substrate SRF(parallel) TN_90° 0 V_T 32.6% 15 V_T 62.2% ΔT 29.6% Rainbow Phenomenon No

EXAMPLE 2

Two SRF substrates were used to manufacture a light modulation device.An alignment film was formed on an electrode layer (ITO (indium tinoxide) layer) of the SRF substrate to prepare a substrate, and twosubstrates were manufactured in the same manner. As the alignment film,one obtained by rubbing a polyimide-based horizontal alignment film(SE-7492, Nissan) having a thickness of 300 nm with a rubbing cloth wasused. Subsequently, a liquid crystal composition, in which 0.519 wt % ofa chiral dopant (S811, Merck) was added to a GHLC composition comprisinga mixture (MDA-16-1235, Merck) of a liquid crystal host having positivedielectric constant anisotropy with refractive index anisotropy (ΔN) of0.13 and a dichroic dye, was disposed between the two substrates as inthe case of Example 1 to prepare a light modulation device. At thistime, the first direction (TD direction, slow axis direction) of thefirst and second substrates was 0 degrees based on the rubbing axis ofthe first substrate, and the orientation directions of the alignmentfilms of the first substrate and the second substrate were each 90degrees. The light modulation device is in an STN mode with a twistedangle of about 270 degrees, the cell gap is about 12 μm, and the ratio(d/p) of cell gap (d) to pitch (p) is about 0.75.

TEST EXAMPLE 4

An electro-optical characteristic and occurrence of a rainbow phenomenonwere evaluated for the light modulation device manufactured in Example2. The electro-optical characteristic was evaluated for the lightmodulation device by measuring a change in transmittance depending onwhether or not a voltage was applied. Specifically, the transmittanceaccording to the applied voltage was measured using a haze meter(NDH5000SP, manufactured by Secos) while an AC power was connected tothe electrode layers (ITO layers) of the first and second substrates anddriven. The transmittance is an average of transmittance for lighthaving a wavelength of 380 nm to 780 nm.

The evaluation of the rainbow phenomenon is a cognitive evaluation, andit has been evaluated that the rainbow phenomenon occurs when two ormore patterns representing different luminance rather than the sameluminance in the sample are generated.

In the following evaluation example, the light modulation devices ofExamples 3 to 8 were manufactured by changing the twisted angle, therefractive index anisotropy of liquid crystals, the cell gap, the dyecontent and the kind of the alignment film.

In the following evaluation example, STN_270° means an STN mode with atwisted angle of 270 degrees, and STN_360° means an STN mode with atwisted angle of 360 degrees. The liquid crystal cell of STN_360° wasprepared by changing the content of the chiral dopant in the liquidcrystal composition of Example 2 to 0.656 wt % and making the rubbingdirections of the alignment films of the first and second substratesanti-parallel to each other, where the ratio (d/p) of the cell gap (d)to the pitch (p) in the STN_360° mode is 0.95.

In the following evaluation example, “0V_T” is the transmittance uponapplying no voltage, “15V_T” is the transmittance upon applying avoltage of 15V, and “ΔT” is a value of “15V_T”-“0V_T.”

TABLE 4 Example 2 Cell Gap 12 μm Δn 0.13 Substrate SRF(parallel)STN_270°  0 V_T 28.0% 15 V_T 62.7% ΔT 34.8% STN_360°  0 V_T 25.0% 15 V_T62.7% ΔT 37.7% Rainbow Phenomenon No

EXAMPLE 3

A light modulation device of Example 3 was manufactured in the samemanner as in Example 2, except that the liquid crystal (MAT-16-969,Merck) having refractive index anisotropy (ΔN) of 0.07 was used as theliquid crystal in Example 2.

The electro-optical characteristic and the occurrence of the rainbowphenomenon were evaluated for Examples 2 and 3, and the results weredescribed in Table 5 below.

TABLE 5 Example 2 Example 3 Cell Gap 12 μm 12 μm Δn 0.13 0.07 SubstrateSRF(parallel) SRF(parallel) STN_270°  0 V_T 28.0% 26.8% 15 V_T 62.7%64.2% ΔT 34.8% 37.4% Rainbow Phenomenon No No

EXAMPLES 4 and 5

Light modulation devices of Examples 4 and 5 were manufactured in thesame manner as in Example 2, except that the refractive index anisotropyof the liquid crystal (using MAT-16-969, Merck), the dye content and thecell gap in Example 2 were changed as shown in Table 5 below.

The electro-optical characteristic and the occurrence of the rainbowphenomenon were evaluated for Examples 4 and 5, and the results weredescribed in Table 6 below.

TABLE 6 Example 4 Example 5 Cell Gap 12 μm 6 μm Δn 0.07 0.07 Dye Content0.94% 2.2% Substrate SRF (parallel) SRF (parallel) STN_360°  0 V_T 26.6%27.3% 15 V_T 66.5% 70.2% ΔT 39.9% 42.9% Rainbow Phenomenon No No

EXAMPLES 6 to 8

Light modulation devices of Examples 6 to 8 were manufactured in thesame manner as in Example 2, except that the refractive index anisotropyof the liquid crystal (using MAT-16-969, Merck), the dye content and thekind of the alignment film in Example 2 were changed as shown in Table 7below. As the vertical alignment film in Examples 7 and 8, SE-5661LB3from Nissan was used.

The electro-optical characteristic and the occurrence of the rainbowphenomenon were evaluated for Examples 6 to 8, and the results weredescribed in Table 7 below. In the following table, the left numericalvalue of ↔ is the transmittance upon applying no voltage, and the rightnumerical value of ↔ means the transmittance upon applying the relevantvoltage.

TABLE 7 Example 6 Example 7 Example 8 Cell Gap 12 μm 12 μm 12 μm Δn 0.070.07 0.07 Dye Content 0.94% 0.94% 1.2% Substrate SRF(parallel)SRF(parallel) SRF(parallel) First Alignment Film Horizontal VerticalVertical Second Alignment Film Horizontal Horizontal Horizontal STN_360°ΔT_5 V 29.2% 31.0% 34.0% [26.2% 

 55.3%] [31.7% 

 62.6%] [26.5% 

 60.5%] ΔT_7 V 34.0% 33.5% 37.2% [26.2% 

 60.2%] [31.7% 

 65.2%] [26.5% 

 63.7%] ΔT_10 V 37.2% 35.3% 38.4% [26.2% 

 63.4%] [31.7% 

 67.0%] [26.5% 

 64.9%] Rainbow Phenomenon No No No

The invention claimed is:
 1. A light modulation device, comprising: afirst polymer film substrate; a second polymer film substrate; an activeliquid crystal layer disposed between the first and second polymer filmsubstrates, wherein the active liquid crystal layer contains a liquidcrystal host and a dichroic dye guest, wherein the active liquid crystallayer is capable of switching between a vertical orientation state and atwisting orientation state upon application of a voltage, each of thefirst and second polymer film substrates has an in-plane retardation of4,000 nm or more for light having a wavelength of 550 nm, wherein eachof the first and second polymer film substrates are stretched films,wherein the stretched films have a machine direction, a transversedirection, and a third direction, wherein the machine direction, thetransverse direction, and the third direction are in-plane directions,wherein the machine direction is perpendicular to the transversedirection, wherein an angle between the third direction and both thetransverse and machine directions ranges from 40 degrees to 50 degrees,wherein each of the first and second polymer films have an elongation(E1) in the transverse direction, an elongation (E2) in the machinedirection, and an elongation (E3) in the third direction, wherein E3 islarger than E1, wherein a ratio of E3 to E2 is 5 or more, and wherein anangle formed by the transverse direction of the first polymer filmsubstrate and the transverse direction of the second polymer filmsubstrate is in a range of 0 degrees to 10 degrees.
 2. The lightmodulation device according to claim 1, wherein the twisting orientationstate is a horizontal twisting orientation state.
 3. The lightmodulation device according to claim 1, wherein each of the first andsecond polymer film substrates is an electrode film substrate having anelectrode layer on one side, and the electrode layers of the first andsecond polymer film substrates face each other.
 4. The light modulationdevice according to claim 1, wherein the first and second polymer filmsubstrates are polyester film substrates.
 5. The light modulation deviceaccording to claim 1, wherein each of the first and second polymer filmsubstrates has a ratio (CTE2/CTE1) of a coefficient of thermal expansion(CTE2) in the machine direction to a coefficient of thermal expansion(CTE1) in the transverse direction of 1.5 or more.
 6. The lightmodulation device according to claim 5, wherein CTE2 is in a range of 50to 100 ppm/° C.
 7. The light modulation device according to claim 1,wherein each of the first and second polymer film substrates has a ratio(YM1/YM2) of an elastic modulus (YM1) in the transverse direction to anelastic modulus (YM2) in the machine direction of 1.5 or more.
 8. Thelight modulation device according to claim 7, wherein YM1 is in a rangeof 2 to 10 GPa.
 9. The light modulation device according to claim 1,wherein each of the first and second polymer film substrates has a ratio(MS1/MS2) of a maximum stress (MS1) in the transverse direction to amaximum stress (MS2) in the machine direction of 1.5 or more.
 10. Thelight modulation device according to claim 9, wherein MS1 is in a rangeof 150 to 250 MPa.
 11. The light modulation device according to claim 1,wherein a twisted angle of the twisting orientation state is more than 0degrees and 360 degrees or less.
 12. Eyewear, comprising: a left eyelens and a right eye lens; and a frame for supporting the left eye lensand the right eye lens, wherein the left eye lens and the right eye lenseach comprise the light modulation device of claim
 1. 13. The lightmodulation device according to claim 1, wherein a ratio of E1 to E2 is 3or more.
 14. The light modulation device according to claim 13, whereineach of the first and second polymer film substrates has E1 of 20% ormore, relative to the respective lengths of the first and second polymerfilm substrates in the transverse direction prior to elongation of thesubstrates in the transverse direction.